I have a question which has been bugging me, maybe you can answer. I understand the concept that the night sky isn't completely white because the light from far distant stars and galaxies hasn't reached us yet.

I was wondering if it has ever been observed that suddenly a star or galaxy has suddenly appeared where there was none the day before because the light has just arrived.

Can you shed any light on this? Or will I have to wait a couple of million years?

Yes,, the speed at which light would arrive on the planet for observation. Yes that is exactly the process

Even our star,, takes 8 minutes and 29 seconds I believe for the light to reach us.

Those that are light years away, when the light finally reaches us. Would to us,, look like a light switch finally came on. Although,, the star itself, would be much older depending on the distance. A blast from the past.

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Tarantula Nebula

These celestial objects are called runaway stars, and they can generally be told apart from other stars via the fact that they move at unjustifiably-high speeds. This particular object, which is no less than 90 times more massive than our own Sun, has been found to be traveling through the outskirts of its home nebula at a speed of about 250,000 miles per hour (400,000 kilometers per hour). According to the group, it could be that the object has been kicked out by its siblings, the other massive stars in the stellar nursery.

The Tarantula Nebula is a highly-active source of new stars, and it is located in the Large Magellanic Cloud, one of our closest neighboring galaxies. Details of the speed and mass of the runaway star have been collected using the new, advanced Cosmic Origins Spectrograph (COS) instrument, which was installed on Hubble last year. The sensitive data collected by COS allowed for astronomers to determine that the large star most likely covered a distance of no less than 375 light-years from its suspected home by now. The experts add that the fireball was most likely produced in a giant star cluster called R136

This explains how some of the other star's,, are kind of kicked into view as well.

There is an astronomical term: "http://en.wikipedia.org/wiki/Nova [Links inactive - To make links active and clickable, login or click here to register]", or "New Star" (plus its big brother: Supernova). However, rather than being the birth of a new star, this represents a sudden nuclear explosion on an old, and previously invisible star.

Galaxies are thought to form through the accretion of many smaller globular clusters over periods longer than the age of the Earth, so they tend to appear very gradually.

An effect called "http://en.wikipedia.org/wiki/Gravitational_microlensing [Links inactive - To make links active and clickable, login or click here to register]" (plus its big brother: Gravitational Lensing) means that a previously-invisible distant star temporarily becomes visible (for a few hours or days) because a dark massive object passes between the star and our telescopes. This causes the light from the distant star to be bent, focusing the light and making it much brighter. These are rare and random events, so they work best with specialised survey telescopes, in orbit.

It is thought that most new stars are formed in http://en.wikipedia.org/wiki/Star_formation [Links inactive - To make links active and clickable, login or click here to register] in the galaxy; the dust shields them from our view until the stellar wind from the new stars eventually disperses it. These events occur over timescales which are quite long in human lifetimes, so they won't suddenly appear.

However, the http://en.wikipedia.org/wiki/James_Webb_Space_Telescope [Links inactive - To make links active and clickable, login or click here to register] is much larger in diameter than Hubble, and operates at much longer infra-red wavelengths, so it will be able to peer into these dense dust clouds, suddenly revealing the new stars inside. It will also be able to see galaxies with extreme red-shifts, suddenly revealing a whole generation of galaxies to our eyes.